unit 1.2 supervised learning.pptx

Machine Learning
Unit I
Supervised Learning
By: Dr. Shweta Saraswat

Contents
• An overview on Machine Learning,
• Types of Machine learning,
• Supervised learning :
• Linear Regression Model
• Naïve Bayes Classifier
• Decision Tree
• K-Nearest Neighbour
• Logistic Regression
• Support Vector Machine
• Random Forest Algorithm

An Overview on Machine Learning
• Definition
• Working of Machine Learning
• Features of Machine Learning
• Importance of Machine Learning

• Machine Learning is said as a subset of artificial
intelligence that is mainly concerned with the
development of algorithms which allow a computer
to learn from the data and past experiences on their
own. The term machine learning was first introduced
by Arthur Samuel in 1959. We can define it in a
summarized way as:

Definition of machine learning
“Machine learning enables a machine to automatically
learn from data, improve performance from
experiences, and predict things without being
explicitly programmed.”

How does Machine Learning work
A Machine Learning system learns from historical data,
builds the prediction models, and whenever it
receives new data, predicts the output for it. The
accuracy of predicted output depends upon the
amount of data, as the huge amount of data helps to
build a better model which predicts the output more
accurately.

How does Machine Learning work

Features of Machine Learning:
• Machine learning uses data to detect various patterns
in a given dataset.
• It can learn from past data and improve
automatically.
• It is a data-driven technology.
• Machine learning is much similar to data mining as it
also deals with the huge amount of the data.

Need for Machine Learning
• The importance of machine learning can be easily
understood by its uses cases, Currently, machine
learning is used in self-driving cars, cyber fraud
detection, face recognition, and friend suggestion by
Facebook, etc. Various top companies such as Netflix
and Amazon have build machine learning models that
are using a vast amount of data to analyze the user
interest and recommend product accordingly.

Following are some key points which show the
importance of Machine Learning:
• Rapid increment in the production of data
• Solving complex problems, which are difficult for a
human
• Decision making in various sector including finance
• Finding hidden patterns and extracting useful
information from data.

Types Of Machine Learning
• The four different types of machine
learning are:
1. Supervised Learning
2. Unsupervised Learning
3. Semi-Supervised Learning
4. Reinforced Learning

#1: Supervised Learning
• In this type of machine learning, machines are
trained using labeled datasets. Machines use this
information to predict output in the future. This
whole process is based on supervision and hence, the
name.
• The core objective of super learning techniques is to
map the input variables with the output variables. It
is extensively used in fraud detection, risk
assessment, and spam filtering.

Here are the Five Common Applications of
Supervised Learning:
1. Image classification and segmentation
2. Disease identification and medical diagnosis
3. Fraud detection
4. Spam detection
5. Speech recognition

#2: Unsupervised Learning
• Unlike the supervised learning technique, here there is no
supervision involved. Unlabeled and unclassified datasets
are used to train the machines. They then predict the
output without supervision or human intervention. This
method is commonly used to bucket or categorize
unsorted data based on their features, similarities, and
differences. Machines are also capable of finding hidden
patterns and trends from the input.

Four Common Applications of Unsupervised
Learning
• Network analysis
• Plagiarism and copyright check
• Recommendations on e-commerce websites
• Detect fraud in bank transactions

#3: Semi-Supervised Learning
• This technique was created keeping the pros and cons of
the supervised and unsupervised learning methods in
mind. During the training period, a combination of labeled
and unlabeled datasets is used to prepare the machines.
However, in the real world, most input datasets are
unlabeled data. This method’s advantage is that it uses all
available data, not only labeled information so it is highly
cost-effective. Firstly, similar data is bucketed. This is done
with the help of an unsupervised learning algorithm. This
helps label all the unlabeled data.

#4: Reinforcement Learning
• In reinforcement learning, there is no concept of labeled
data. Machines learn only from experiences. Using a trial
and error method, learning works on a feedback-based
process. The AI explores the data, notes features, learns
from prior experience, and improves its overall
performance. The AI agent gets rewarded when the
output is accurate. And punished when the results are not
favorable.

How is Reinforcement Training Used in the Real
World?
• Building intelligent robots
• Video games and interactive content
• Learn and schedule resources
• Text Mining

Supervised Machine Learning
• Definition
• Working with Example
• Steps involved in Supervised Learning
• Types of supervised learning
• Advantages
• Disadvantages

Supervised Machine Learning: Definition
• Supervised learning is the types of machine learning
in which machines are trained using well "labelled"
training data, and on basis of that data, machines
predict the output. The labelled data means some
input data is already tagged with the correct output.

How Supervised Learning Works?
• In supervised learning, models are trained using
labelled dataset, where the model learns about each
type of data. Once the training process is completed,
the model is tested on the basis of test data (a subset
of the training set), and then it predicts the output.

The working of Supervised learning can be
easily understood by the below example and
diagram:

Suppose we have a dataset of different types of
shapes which includes square, rectangle,
triangle, and Polygon..
• Now the first step is that we need to train the model for
each shape
• If the given shape has four sides, and all the sides are
equal, then it will be labelled as a Square.
• If the given shape has three sides, then it will be labelled
as a triangle.
• If the given shape has six equal sides then it will be
labelled as hexagon.

Working with example
• Now, after training, we test our model using the test
set, and the task of the model is to identify the shape.
• The machine is already trained on all types of shapes,
and when it finds a new shape, it classifies the shape
on the bases of a number of sides, and predicts the
output.

Steps Involved in Supervised Learning:
• First Determine the type of training dataset
• Collect/Gather the labelled training data.
• Split the training dataset into training dataset, test dataset, and validation
dataset.
• Determine the input features of the training dataset, which should have
enough knowledge so that the model can accurately predict the output.
• Determine the suitable algorithm for the model, such as support vector
machine, decision tree, etc.
• Execute the algorithm on the training dataset. Sometimes we need
validation sets as the control parameters, which are the subset of training
datasets.
• Evaluate the accuracy of the model by providing the test set. If the model
predicts the correct output, which means our model is accurate.

Types of supervised Machine learning
Algorithms:

1. Regression
• Regression algorithms are used if there is a
relationship between the input variable and the
output variable. It is used for the prediction of
continuous variables, such as Weather forecasting,
Market Trends, etc.

Below are some popular Regression algorithms
which come under supervised learning:
• Linear Regression
• Regression Trees
• Non-Linear Regression
• Bayesian Linear Regression
• Polynomial Regression

2. Classification
• Classification algorithms are used when the output
variable is categorical, which means there are two classes
such as Yes-No, Male-Female, True-false, etc.
• Random Forest
• Decision Trees
• Logistic Regression
• Support vector Machines

Advantages of Supervised learning:
• With the help of supervised learning, the model can
predict the output on the basis of prior experiences.
• In supervised learning, we can have an exact idea
about the classes of objects.
• Supervised learning model helps us to solve various
real-world problems such as fraud detection, spam
filtering, etc.

Disadvantages of supervised learning:
• Supervised learning models are not suitable for handling
the complex tasks.
• Supervised learning cannot predict the correct output if
the test data is different from the training dataset.
• Training required lots of computation times.
• In supervised learning, we need enough knowledge about
the classes of object.
•

Linear Regression in Machine
Learning
• Definition
• Explanation
• Linear Regression model
• Types of linear regression
• Linear regression line
• Finding the best fit line
• Cost function

Definition
• Linear regression algorithm shows a linear
relationship between a dependent (y) and one or
more independent (y) variables, hence called as
linear regression. Since linear regression shows the
linear relationship, which means it finds how the
value of the dependent variable is changing according
to the value of the independent variable.

explanation
• Linear regression is one of the easiest and most
popular Machine Learning algorithms. It is a statistical
method that is used for predictive analysis. Linear
regression makes predictions for continuous/real or
numeric variables such as sales, salary, age, product
price, etc.

Linear Regression model
• The linear regression model provides a sloped
straight line representing the relationship between
the variables. Consider the below image:

Linear Regression model
Mathematically, we can represent a linear regression as:
y= a0+a1x+ ε
Here,
Y= Dependent Variable (Target Variable)
X= Independent Variable (predictor Variable)
a0= intercept of the line (Gives an additional degree of freedom)
a1 = Linear regression coefficient (scale factor to each input value).
ε = random error
The values for x and y variables are training datasets for Linear
Regression model representation.
y= a0+a1x+ ε

Types of Linear Regression
1. Simple Linear Regression:
If a single independent variable is used to predict the
value of a numerical dependent variable, then such a
Linear Regression algorithm is called Simple Linear
Regression.
2. Multiple Linear regression:
If more than one independent variable is used to predict
the value of a numerical dependent variable, then such
a Linear Regression algorithm is called Multiple Linear
Regression.

Linear Regression Line
• A linear line showing the relationship between the
dependent and independent variables is called
a regression line. A regression line can show two
types of relationship:

Positive Linear Relationship:
• If the dependent variable increases on the Y-axis and
independent variable increases on X-axis, then such a
relationship is termed as a Positive linear
relationship.

Negative Linear Relationship:
• If the dependent variable decreases on the Y-axis and
independent variable increases on the X-axis, then
such a relationship is called a negative linear
relationship.
•

Finding the best fit line:
• When working with linear regression, our main goal is
to find the best fit line that means the error between
predicted values and actual values should be
minimized. The best fit line will have the least error.
• The different values for weights or the coefficient of
lines (a0, a1) gives a different line of regression, so we
need to calculate the best values for a0 and a1 to find
the best fit line, so to calculate this we use cost
function.

Cost function-
• The different values for weights or coefficient of lines (a0, a1) gives
the different line of regression, and the cost function is used to
estimate the values of the coefficient for the best fit line.
• Cost function optimizes the regression coefficients or weights. It
measures how a linear regression model is performing.
• We can use the cost function to find the accuracy of the mapping
function, which maps the input variable to the output variable. This
mapping function is also known as Hypothesis function.
• For Linear Regression, we use the Mean Squared Error (MSE) cost
function, which is the average of squared error occurred between
the predicted values and actual values

Naïve Bayes Classifier Algorithm
• Definition
• Explanation
• Why it is called Naïve Bayes
• Bayes Theorem
• Working of Naïve Bayes Classifier
• Applying Bayes Theorem
• Advantages and disadvantages
• Applications
• Types of Naïve Bayes Model

Definition
• Naïve Bayes Classifier is one of the simple and most
effective Classification algorithms which helps in
building the fast machine learning models that can
make quick predictions.

Explanation
• Naïve Bayes algorithm is a supervised learning algorithm,
which is based on Bayes theorem and used for solving
classification problems.
• It is mainly used in text classification that includes a high-
dimensional training dataset.
• It is a probabilistic classifier, which means it predicts on
the basis of the probability of an object.
• Some popular examples of Naïve Bayes Algorithm
are spam filtration, Sentimental analysis, and classifying
articles.

Why is it called Naïve Bayes?
• The Naïve Bayes algorithm is comprised of two words
Naïve and Bayes, Which can be described as:
• Naïve: It is called Naïve because it assumes that the
occurrence of a certain feature is independent of the
occurrence of other features. Such as if the fruit is
identified on the bases of color, shape, and taste, then red,
spherical, and sweet fruit is recognized as an apple. Hence
each feature individually contributes to identify that it is
an apple without depending on each other.
• Bayes: It is called Bayes because it depends on the
principle of Bayes' Theorem.

Working of Naïve Bayes' Classifier:
• Working of Naïve Bayes' Classifier can be understood with the
help of the below example:
• Suppose we have a dataset of weather conditions and
corresponding target variable "Play". So using this dataset we
need to decide that whether we should play or not on a
particular day according to the weather conditions. So to solve
this problem, we need to follow the below steps:
• Convert the given dataset into frequency tables.
• Generate Likelihood table by finding the probabilities of given
features.
• Now, use Bayes theorem to calculate the posterior probability.

Problem: If the weather is
sunny,then the Player
should play or not?
• Solution: To solve this, first
consider
the dataset:
Outlook Play
0 Rainy Yes
1 Sunny Yes
2 Overcast Yes
3 Overcast Yes
4 Sunny No
5 Rainy Yes
6 Sunny Yes
7 Overcast Yes
8 Rainy No
9 Sunny No
10 Sunny Yes

Frequency table for the Weather Conditions:
Weather Yes No
Overcast 5 0
Rainy 2 2
Sunny 3 2
Total 10 5

Likelihood table weather condition:
Weather No Yes
Overcast 0 5 5/14= 0.35
Rainy 2 2 4/14=0.29
Sunny 2 3 5/14=0.35
All 4/14=0.29 10/14=0.71

Advantages of Naïve Bayes Classifier:
• Naïve Bayes is one of the fast and easy ML algorithms
to predict a class of datasets.
• It can be used for Binary as well as Multi-class
Classifications.
• It performs well in Multi-class predictions as
compared to the other Algorithms.
• It is the most popular choice for text classification
problems.

Disadvantages of Naïve Bayes Classifier:
• Naive Bayes assumes that all features are
independent or unrelated, so it cannot learn the
relationship between features.

Applications of Naïve Bayes Classifier:
• It is used for Credit Scoring.
• It is used in medical data classification.
• It can be used in real-time predictions because Naïve
Bayes Classifier is an eager learner.
• It is used in Text classification such as Spam
filtering and Sentiment analysis.

Types of Naïve Bayes Model:
• There are three types of Naive Bayes Model, which are given below:
• Gaussian: The Gaussian model assumes that features follow a normal distribution. This
means if predictors take continuous values instead of discrete, then the model
assumes that these values are sampled from the Gaussian distribution.
• Multinomial: The Multinomial Naïve Bayes classifier is used when the data is
multinomial distributed. It is primarily used for document classification problems, it
means a particular document belongs to which category such as Sports, Politics,
education, etc.
The classifier uses the frequency of words for the predictors.
• Bernoulli: The Bernoulli classifier works similar to the Multinomial classifier, but the
predictor variables are the independent Booleans variables. Such as if a particular
word is present or not in a document. This model is also famous for document
classification tasks.

Decision Tree
• Definition
• Explanation
• Why use Decision Tree?
• Decision tree terminologies
• Working
• Example
• Attribute Selection Measure
• Advantages and disadvantages

Definition
• Decision Tree is a Supervised learning technique that
can be used for both classification and Regression
problems, but mostly it is preferred for solving
Classification problems. It is a tree-structured
classifier, where internal nodes represent the features
of a dataset, branches represent the decision
rules and each leaf node represents the outcome.

Explanation
• In a Decision tree, there are two nodes, which are the Decision Node and Leaf
Node. Decision nodes are used to make any decision and have multiple branches,
whereas Leaf nodes are the output of those decisions and do not contain any further
branches.
• The decisions or the test are performed on the basis of features of the given dataset.
• It is a graphical representation for getting all the possible solutions to a
problem/decision based on given conditions.
• It is called a decision tree because, similar to a tree, it starts with the root node, which
expands on further branches and constructs a tree-like structure.
• In order to build a tree, we use the CART algorithm, which stands for Classification and
Regression Tree algorithm.
• A decision tree simply asks a question, and based on the answer (Yes/No), it further
split the tree into subtrees.

General Structure of Decision Tree

Why use Decision Trees?
• There are various algorithms in Machine learning, so
choosing the best algorithm for the given dataset and
problem is the main point to remember while creating a
machine learning model. Below are the two reasons for
using the Decision tree:
• Decision Trees usually mimic human thinking ability while
making a decision, so it is easy to understand.
• The logic behind the decision tree can be easily
understood because it shows a tree-like structure.

Decision Tree Terminologies
• Root Node: Root node is from where the decision tree starts. It
represents the entire dataset, which further gets divided into two or
more homogeneous sets.
• Leaf Node: Leaf nodes are the final output node, and the tree
cannot be segregated further after getting a leaf node.
• Splitting: Splitting is the process of dividing the decision node/root
node into sub-nodes according to the given conditions.
• Branch/Sub Tree: A tree formed by splitting the tree.
• Pruning: Pruning is the process of removing the unwanted branches
from the tree.
• Parent/Child node: The root node of the tree is called the parent
node, and other nodes are called the child nodes.

How does the Decision Tree algorithm Work?
• Step-1: Begin the tree with the root node, says S, which contains the
complete dataset.
• Step-2: Find the best attribute in the dataset using Attribute Selection
Measure (ASM).
• Step-3: Divide the S into subsets that contains possible values for the best
attributes.
• Step-4: Generate the decision tree node, which contains the best attribute.
• Step-5: Recursively make new decision trees using the subsets of the dataset
created in step -3. Continue this process until a stage is reached where you
cannot further classify the nodes and called the final node as a leaf node.

• Example: Suppose there is a candidate who has a job offer
and wants to decide whether he should accept the offer or
Not. So, to solve this problem, the decision tree starts with
the root node (Salary attribute by ASM). The root node
splits further into the next decision node (distance from
the office) and one leaf node based on the corresponding
labels. The next decision node further gets split into one
decision node (Cab facility) and one leaf node. Finally, the
decision node splits into two leaf nodes (Accepted offers
and Declined offer). Consider the below diagram:

Attribute Selection Measures
• While implementing a Decision tree, the main issue arises
that how to select the best attribute for the root node and
for sub-nodes. So, to solve such problems there is a
technique which is called as Attribute selection measure or
ASM. By this measurement, we can easily select the best
attribute for the nodes of the tree. There are two popular
techniques for ASM, which are:
• Information Gain
• Gini Index

Advantages of the Decision Tree
• It is simple to understand as it follows the same process
which a human follow while making any decision in real-
life.
• It can be very useful for solving decision-related problems.
• It helps to think about all the possible outcomes for a
problem.
• There is less requirement of data cleaning compared to
other algorithms.

Disadvantages of the Decision Tree
• The decision tree contains lots of layers, which makes
it complex.
• It may have an overfitting issue, which can be
resolved using the Random Forest algorithm.
• For more class labels, the computational complexity
of the decision tree may increase.

K-Nearest Neighbour Algorithm
• Definition
• Explanation
• Example
• Need of K-NN algorithm
• Working
• How to select value of K
• Advantages
• Disadvantages

Definition
• K-Nearest Neighbour is one of the simplest Machine
Learning algorithms based on Supervised Learning
technique which assumes the similarity between the
new case/data and available cases and put the new
case into the category that is most similar to the
available categories.

Explanation
• K-NN algorithm stores all the available data and classifies a new data point
based on the similarity. This means when new data appears then it can be
easily classified into a well suite category by using K- NN algorithm.
• K-NN algorithm can be used for Regression as well as for Classification but
mostly it is used for the Classification problems.
• K-NN is a non-parametric algorithm, which means it does not make any
assumption on underlying data.
• It is also called a lazy learner algorithm because it does not learn from the
training set immediately instead it stores the dataset and at the time of
classification, it performs an action on the dataset.
• KNN algorithm at the training phase just stores the dataset and when it gets
new data, then it classifies that data into a category that is much similar to
the new data.

How to select the value of K in the K-NN
Algorithm?
• There is no particular way to determine the best
value for "K", so we need to try some values to find
the best out of them. The most preferred value for K
is 5.
• A very low value for K such as K=1 or K=2, can be
noisy and lead to the effects of outliers in the model.
• Large values for K are good, but it may find some
difficulties.

Advantages of KNN Algorithm:
• It is simple to implement.
• It is robust to the noisy training data
• It can be more effective if the training data is large.

Disadvantages of KNN Algorithm:
• Always needs to determine the value of K which may
be complex some time.
• The computation cost is high because of calculating
the distance between the data points for all the
training samples.

Logistic Regression
• Definition
• Explanation
• Example
• Logistic Function
• Logistic Regression Assumption
• Equation
• Types

Definition
• Logistic regression is one of the most popular
Machine Learning algorithms, which comes under the
Supervised Learning technique. It is used for
predicting the categorical dependent variable using a
given set of independent variables.

Explanation
• Logistic regression predicts the output of a categorical dependent variable.
Therefore the outcome must be a categorical or discrete value. It can be either Yes
or No, 0 or 1, true or False, etc. but instead of giving the exact value as 0 and 1, it
gives the probabilistic values which lie between 0 and 1.
• Logistic Regression is much similar to the Linear Regression except that how they
are used. Linear Regression is used for solving Regression problems,
whereas Logistic regression is used for solving the classification problems.
• In Logistic regression, instead of fitting a regression line, we fit an "S" shaped
logistic function, which predicts two maximum values (0 or 1).
• The curve from the logistic function indicates the likelihood of something such as
whether the cells are cancerous or not, a mouse is obese or not based on its
weight, etc.
• Logistic Regression is a significant machine learning algorithm because it has the
ability to provide probabilities and classify new data using continuous and discrete
datasets.

Logistic Function (Sigmoid Function):
• The sigmoid function is a mathematical function used to
map the predicted values to probabilities.
• It maps any real value into another value within a range of
0 and 1.
• The value of the logistic regression must be between 0 and
1, which cannot go beyond this limit, so it forms a curve
like the "S" form. The S-form curve is called the Sigmoid
function or the logistic function.
• In logistic regression, we use the concept of the threshold
value, which defines the probability of either 0 or 1. Such
as values above the threshold value tends to 1, and a
value below the threshold values tends to 0.

Assumptions for Logistic Regression:
• The dependent variable must be categorical in
nature.
• The independent variable should not have multi-
collinearity.

Support Vector Machine
Definition
Explanation
Example
Types of SVM
Hyperplane and support vectors in SVM
Working in Linear SVM
Working in Non-linear SVM

Support Vector Machine
Definition
Support Vector Machine or SVM is one of the most
popular Supervised Learning algorithms, which is
used for Classification as well as Regression
problems. However, primarily, it is used for
Classification problems in Machine Learning.

Explanation
• The goal of the SVM algorithm is to create the best line or
decision boundary that can segregate n-dimensional space
into classes so that we can easily put the new data point in
the correct category in the future. This best decision
boundary is called a hyperplane.
• SVM chooses the extreme points/vectors that help in
creating the hyperplane. These extreme cases are called as
support vectors, and hence algorithm is termed as
Support Vector Machine. Consider the below diagram in
which there are two different categories that are classified
using a decision boundary or hyperplane:

Example:
• SVM can be understood with the example that we have used in
the KNN classifier. Suppose we see a strange cat that also has
some features of dogs, so if we want a model that can
accurately identify whether it is a cat or dog, so such a model
can be created by using the SVM algorithm. We will first train
our model with lots of images of cats and dogs so that it can
learn about different features of cats and dogs, and then we test
it with this strange creature. So as support vector creates a
decision boundary between these two data (cat and dog) and
choose extreme cases (support vectors), it will see the extreme
case of cat and dog. On the basis of the support vectors, it will
classify it as a cat. Consider the below diagram::

Types of SVM
• SVM can be of two types:
• Linear SVM: Linear SVM is used for linearly separable
data, which means if a dataset can be classified into
two classes by using a single straight line, then such
data is termed as linearly separable data, and classifier
is used called as Linear SVM classifier.
• Non-linear SVM: Non-Linear SVM is used for non-
linearly separated data, which means if a dataset
cannot be classified by using a straight line, then such
data is termed as non-linear data and classifier used is
called as Non-linear SVM classifier.

Hyperplane and Support Vectors in the SVM
algorithm:
• Hyperplane: There can be multiple lines/decision boundaries to segregate the
classes in n-dimensional space, but we need to find out the best decision
boundary that helps to classify the data points. This best boundary is known as
the hyperplane of SVM.
• The dimensions of the hyperplane depend on the features present in the
dataset, which means if there are 2 features (as shown in image), then
hyperplane will be a straight line. And if there are 3 features, then hyperplane
will be a 2-dimension plane.
• We always create a hyperplane that has a maximum margin, which means the
maximum distance between the data points.
• Support Vectors:
• The data points or vectors that are the closest to the hyperplane and which
affect the position of the hyperplane are termed as Support Vector. Since
these vectors support the hyperplane, hence called a Support vector.

How does SVM works?
• Linear SVM:The working of the SVM algorithm can be
understood by using an example. Suppose we have a
dataset that has two tags (green and blue), and the
dataset has two features x1 and x2. We want a
classifier that can classify the pair(x1, x2) of
coordinates in either green or blue. Consider the
below image:

• Hence, the SVM algorithm helps to find the best
line or decision boundary; this best boundary or
region is called as a hyperplane. SVM algorithm
finds the closest point of the lines from both
the classes. These points are called support
vectors. The distance between the vectors and
the hyperplane is called as margin. And the goal
of SVM is to maximize this margin.
The hyperplane with maximum margin is called
the optimal hyperplane.

Non-Linear SVM:
• If data is linearly arranged, then we can separate it
by using a straight line, but for non-linear data, we
cannot draw a single straight line. Consider the
below image:
So to separate these data points, we need to add one more dimension. For linear data, we
have used two dimensions x and y, so for non-linear data, we will add a third
dimension z. It can be calculated as:
z=x2 +y2

So now, SVM will divide the datasets into classes in the
following way. Consider the below image:
By adding the third dimension, the sample space will
become as below image

Random Forest Algorithm
• Definition
• Explanation
• Example
• Assumptions For Random Forest
• Why Use Random Forest?
• Working
• Applications
• Advantages
• Disadvantages

Definition
• Random Forest is a popular machine learning
algorithm that belongs to the supervised learning
technique. It can be used for both Classification and
Regression problems in ML. It is based on the concept
of ensemble learning, which is a process
of combining multiple classifiers to solve a complex
problem and to improve the performance of the
model.

Explanation
• As the name suggests, "Random Forest is a classifier that
contains a number of decision trees on various subsets of
the given dataset and takes the average to improve the
predictive accuracy of that dataset." Instead of relying on
one decision tree, the random forest takes the prediction
from each tree and based on the majority votes of
predictions, and it predicts the final output.
• The greater number of trees in the forest leads to higher
accuracy and prevents the problem of overfitting.

What is overfitting
• Overfitting occurs when our machine learning model tries to cover all the data points
or more than the required data points present in the given dataset. Because of this,
the model starts caching noise and inaccurate values present in the dataset, and all
these factors reduce the efficiency and accuracy of the model. The overfitted model
has low bias and high variance.
• Signal: It refers to the true underlying pattern of the data that helps the machine
learning model to learn from the data.
• Noise: Noise is unnecessary and irrelevant data that reduces the performance of the
model.
• Bias: Bias is a prediction error that is introduced in the model due to oversimplifying
the machine learning algorithms. Or it is the difference between the predicted values
and the actual values.
• Variance: If the machine learning model performs well with the training dataset, but
does not perform well with the test dataset, then variance occurs.

Assumptions for Random Forest
• Since the random forest combines multiple trees to predict
the class of the dataset, it is possible that some decision
trees may predict the correct output, while others may not.
But together, all the trees predict the correct output.
Therefore, below are two assumptions for a better Random
forest classifier:
• There should be some actual values in the feature variable
of the dataset so that the classifier can predict accurate
results rather than a guessed result.
• The predictions from each tree must have very low
correlations.

Why use Random Forest?
• Below are some points that explain why we should use the
Random Forest algorithm:
• It takes less training time as compared to other algorithms.
• It predicts output with high accuracy, even for the large
dataset it runs efficiently.
• It can also maintain accuracy when a large proportion of
data is missing.

How does Random Forest algorithm work?
• Random Forest works in two-phase first is to create the random forest by
combining N decision tree, and second is to make predictions for each tree
created in the first phase.
• The Working process can be explained in the below steps and diagram:
• Step-1: Select random K data points from the training set.
• Step-2: Build the decision trees associated with the selected data points (Subsets).
• Step-3: Choose the number N for decision trees that you want to build.
• Step-4: Repeat Step 1 & 2.
• Step-5: For new data points, find the predictions of each decision tree, and assign
the new data points to the category that wins the majority votes.

Example: Suppose there is a dataset that contains
multiple fruit images. So, this dataset is given to the
Random forest classifier. The dataset is divided into
subsets and given to each decision tree. During the
training phase, each decision tree produces a
prediction result, and when a new data point occurs,
then based on the majority of results, the Random
Forest classifier predicts the final decision. Consider
the below image:

Applications of Random Forest
• There are mainly four sectors where Random forest mostly used:
• Banking: Banking sector mostly uses this algorithm for the
identification of loan risk.
• Medicine: With the help of this algorithm, disease trends and risks of
the disease can be identified.
• Land Use: We can identify the areas of similar land use by this
algorithm.
• Marketing: Marketing trends can be identified using this algorithm.

Advantages of Random Forest
• Random Forest is capable of performing both
Classification and Regression tasks.
• It is capable of handling large datasets with
high dimensionality.
• It enhances the accuracy of the model and
prevents the overfitting issue.

Disadvantages of Random Forest
• Although random forest can be used for both
classification and regression tasks, it is not more
suitable for Regression tasks.

Book Reference
118
S. No. Title of Book Authors Publisher
Reference Books
T1 Pattern Recognition and Machine
Learning
Christopher M. Bishop Springer
T2 Introduction to Machine Learning
(Adaptive Computation and
Machine Learning),
Ethem Alpaydın MIT Press
Text Books
R1 Machine Learning Mitchell. T, McGraw Hill

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